The long range goal of this project is to identify factors which contribute to variations in salt (NaCl) intake and preference. Salt preference refers to the ingestion of sodium or NaCl in excess of physiological need and is of particular interest because high salt intake has been implicated in the development and maintenance of essential hypertension in humans. Two models have been identified in which rats show significant departures from the "species typical norm" of salt preference. One, the neonatal rat, freely ingests NaCl solutions as high as 2% and 41% which are avoided by adult rats. In contrast, an inbred strain, the Fischer-344 (F-344) rat, fails to prefer even isotonic or hypotonic NaCl solutions to water. These two models represent opposite extremes on a continuum of salt preference. Electrophysiological, surgical and behavioral approaches will be utilized to define the gustatory mechanisms which underlie these behaviors. A focus of this proposal is the hypothesis that strain and age differences in amiloride-sensitive sodium transport at the taste bud contribute to wide variations in salt preference. Electrophysiological recordings of multiunit activity of the chorda tympani nerve in response to NaCl stimuli, before and after amiloride pretreatment, will be used to assess amiloride-sensitive sodium transport mechanisms. This approach will be combined with a genetic one, cosegregation analysis, to evaluate the role of enhanced amiloride-sensitvity of taste buds in the NaCl aversion of F-344 rats. Transection of the chorda tympani nerve, which has been found to dramatically eliminate the NaCl aversion of F-344 rats, will be employed to assess the contribution of peripheml gustatory signals to NaCl preference and intake. Behavioral studies will include intraoral infusions in neonatal rats; measures of licking behavior to NaCl solutions in brief access tests as well as traditional two-bottle preference testing methods.